Photosynthetic pigments of sandy sediments on the north Mediterranean coast: their spatial distribution and its effect on sampling strategies

Benthic microalgae (BMA) are important primary producers constituting an essential component of nearshore food webs. BMA also release extracellular polymeric secretions that stabilize sediments. Primary objectives of our research were to assess the separate and interactive effects of biotic and abiotic disturbances on structure and spatial patterns of microalgal communities in shallow-water sediments. Using field comparative studies, we characterized the effects of 2 prominent types of disturbance: macroinvertebrate ingestion and tidal resuspension. BMA biomass and composition in fecal materials from the enteropneust Balanoglossus aurantiacus and sediments were followed through time using fluorometry and molecular techniques (PCR-DGGE analysis of 18S rDNA and sequencing). We also examined the effects of disturbance on spatial patterns of BMA biomass, diversity, and composition over the larger sedimentary landscape using correlative studies. Deposit-feeder ingestion was found to significantly reduce BMA biomass and alter BMA composition, although qualitative changes were comparatively less remarkable. A significant difference was also found between average biomass before and after tidal immersion. Spatial autocorrelation revealed heterogeneity in BMA distribution during low tide, and that this spatial patterning correlated with B. aurantiacus fecal coils. Samples taken after tidal immersion showed no patchiness, nor was there a correlation between BMA biomass and pre-immersion fecal cover. In intertidal sediments, the qualitative and quantitative impacts of deposit feeding, and the resulting landscape-scale patchiness, appear to be short-lived due to erasure by frequent tidal resuspension.

Section: Discussioncontrasting

confidence: 51%

Interacting effects of deposit feeding and tidal resuspension on benthic microalgal community structure and spatial patterns

Plante¹,

Frank²,

Roth³

2011

“…At the station scale, which was the microscale, specific assemblages remained similar in relation to the granulometric character of the sediment (Plante et al 1986, Saburova et al 1995. Thus, only 1 sediment core was collected for granulometry analysis and water content while a second core was used to analyse species diversity.…”

Section: Methodsmentioning

confidence: 99%

“…To assess microphytobenthic structure at the mesoscale during 15 mo, sampling was distributed over stations and included a few sampling units per station, as recommended by Plante et al (1986) and Saburova et al (1995). Thus 5 stations from a transect were sampled monthly at low tide between May 2000 and July 2001 (Fig.…”

Section: Methodsmentioning

confidence: 99%

Spatio-temporal changes in microphytobenthos structure analysed by pigment composition in a macrotidal flat (Bourgneuf Bay, France)

Méléder¹,

Barillé²,

Rincé³

et al. 2005

The aim of this study was to contribute to a better understanding of turbid coastal ecosystems, focusing on spatio-temporal changes at the mesoscale in microphytobenthos structures in a macrotidal bay (Bourgneuf, France). This was based on pigment analysis by high-pressure liquid chromatography (HPLC), reinforced by microscopy observations, in relation to sediment characteristics. Microphytobenthos assemblages of this mudflat were 97% dominated by diatoms, confirmed by HPLC analysis, which showed biomarker pigments of this group: chlorophyll c, fucoxanthin, diadinoxanthin and diatoxanthin. The main assemblage is constituted of epipsammic species, like Plagiogrammopsis, Achnanthes and Cocconeis, characterising mixed sediments. However, this could be replaced by epipelic species, like Plagiotropis, Pleurosigma and Staurophora, during summer due to station silting. Microphytobenthic photosynthetic active biomass in the first 2 mm varied spatially and temporally from 12.2 to 186.9 mg chl a m -2. The predominance of a biomass spatial variability reflected spatial changes in sediment grain size and water content. Biomass in the first 2 mm represented from 28 to 68% of the total amount in the first 10 mm. This indicated an accumulation of biomass in illuminated layers and a biomass decrease with depth associated with increasing values of the ratio of phaeopigments a and fucoxanthin to chlorophyll a (phaeo a/chl a and fuco/chl a). Both could exceed 1.00 in deeper layers. Temporal changes in microphytobenthos structure at the mesoscale were mainly linked to hydrodynamism. This is stronger in winter and responsible for allochthonous pigment input (lutein and phaeophytin b) and sediment mixing, as grazing activity by macro-and meiofauna, forming chlorophyll a breakdown products, is responsible for an increase in fuco/chl a and phaeo a/chl a values during spring/summer. KEY WORDS: Microphytobenthos · Diatoms · Pigments · High-pressure liquid chromatography · HPLC · GranulometryResale or republication not permitted without written consent of the publisher

“…The distribution of MPB is, however, extremely patchy over space (Admiraal 1984, Saburova et al 1995, Seuront & Spilmont 2002 and time (MacIntyre & Cullen 1995, Serodio et al 1997. Variability in distribution is governed by many diverse biotic and abiotic processes, including diel rhythms of vertical migration (Consalvey et al 2004), hydrodynamic factors (Safi 2003), size of sediment grains (Colijn & Dijkema 1981), salinity and nutrient gradients (Underwood et al 1998), small-scale variations in topography (Plante et al 1986), and shading (Stutes et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Spatial variation of chlorophyll on estuarine mudflats determined by field-based remote sensing

Murphy¹,

Tolhurst²,

Chapman³

et al. 2008

We present an approach to field-based remote sensing of the spatial variation of chlorophyll (as an index of microphytobenthic biomass) in intertidal soft sediments using digital colourinfrared imagery. Variation in amounts of chlorophyll a was quantified from small (cm) to large (100 m) scales within a single tidal cycle, using levels of replication and resolution that would be difficult to achieve using conventional sampling strategies. Eight scales of interest were selected: 100, 50, 2 and 1 m, and 40, 8, 4 and < 2 cm. These scales have been associated with variability in chlorophyll in previous studies. The fully hierarchical design allowed spatial variance to be estimated independently at each chosen spatial scale. Data were collected along 2 replicate transects at 2 locations within each of 2 different estuaries. A strong linear relationship was found between measured chlorophyll and image estimates of chlorophyll. Replicate transects in 2 of the 4 locations showed similar patterns of variability across spatial scales. Relatively large amounts of variability were found at the smallest spatial scales (4 and < 2 cm) and at the 40 cm scale, but the 8 cm scale was an unimportant source of variation. At some scales, transects gave similar results, providing generality to the conclusions reached. At other scales, transects gave quite different results, drawing attention to problems of inferring ecological processes when there are only single sets of data. Large differences in variability were also found from location to location. These patterns suggest that spatial variability is governed by complex interactions between fauna, microflora and sediment.